The present invention relates to a band gap circuit in which an operation is performed in a high-frequency region by employing a low-voltage power supply.
Conventionally, a semiconductor integrated circuit is provided with a reference voltage generation circuit for stably generating a reference voltage for use in a D/A converter etc. As to the reference voltage generation circuit, there is a band gap circuit in which a difference of a threshold voltage of a transistor is utilized. The band gap circuit prevents the semiconductor integrated circuit from malfunctioning due to the rising of the voltage that occurs at the time of introducing the power supply of the semiconductor integrated circuit, and fluctuation etc. of a power supply voltage that occurs during the operation, and reduces power supply voltage dependency of the semiconductor integrated circuit. Also, this band gap circuit also generates the reference voltage stabilized against temperature to reduce temperature dependency of the reference voltage.
In recent years, high speed processing of a logic circuit employing the low-voltage power supply has been performed, and the high-speed processing has been performed in the order of GHz. Power supply noise in 5% or something like this is actualized in performing the high-speed processing of the logic circuit employing the low-voltage power in such a manner, and the band gap circuit having an excellent PSRR (Power Supply Rejection Ratio) has been required more positively than it was required so far.
As the band gap circuit that corresponds to the semiconductor integrated circuit to which the voltage is applied by the low-voltage power supply and which is driven at a high speed, are known a current-mirror band gap circuit employing a current mirror, a differential band gap circuit employing a differential amplifier, and the like, for example, as described in “A Precise On-Chip Voltage Generator for a Gigascale DRAM with a Negative Word-Line Scheme”, IEEE JOURNAL OF SOLID-STATE CIRCUITS. VOL. 34. NO. 8. AUGUST 1999. The current-mirror band gap circuit and the differential band gap circuit like this will be explained by referring to the accompanied drawings.
As shown in FIG. 8, the current-mirror band gap circuit has a p-type transistor P11, a p-type transistor P12, an n-type transistor N11, and an n-type transistor N12. A p-type transistor P13 has its gate connected between the n-type transistor N12 and the p-type transistor P12 in this current-mirror band gap circuit.
Furthermore, as shown in FIG. 8, in this current-mirror band gap circuit, a resistor R11 and a diode D12 are connected between the n-type transistor N12 and a negative power supply point. And, a resistor R12 and a diode D13 are connected between an output terminal VOUT and the negative power supply. Furthermore, the diode D11 is connected between the n-type transistor N11 and the negative power supply. Also, these resistors R11 and R12, and diodes D12 and D13 have a function of discharging a current that transitionally flows into the output terminal VOUT at the time of introducing the power supply and of fluctuation thereof.
FIG. 9 is one example of a characteristic view illustrating power supply voltage dependency in the current-mirror band gap circuit. In FIG. 9, a power supply voltage VDD was set in a transverse axis, and a voltage of an output terminal VOUT in an axis of ordinates. As shown in FIG. 9, it is necessary to apply an input voltage VDD of at least approx. 1.5 V to an input terminal in operating the conventional current-mirror band gap circuit. At this time, the current-mirror band gap circuit operates with the output voltage VOUT thereof at approx. 1.25 V.
FIG. 10 illustrates the conventional differential band gap circuit. As shown in FIG. 10, the differential band gap circuit has a differential amplifier to be configured of a pair of p-type transistors P1 and P2, and a pair of n-type transistors N1 and N2. This differential amplifier has the gate of p-type transistor P3 connected between the p-type transistor P2 and the n-type transistor N2 thereof, and this p-type transistor P3 is connected to the output terminal VOUT.
The resistor R2, and the resistor R1 and the diode D1, which are connected between this resistor R2 and the ground, are connected to the output terminal VOUT in this order. Also, as shown in FIG. 10, in addition to these resistors R1 and R2 and the diode D1, the resistor R3 and the diode D2 are connected between the output terminal VOUT and the ground in this order. A noninverting terminal of the differential amplifier is connected between the resistor R1 and the resistor R2, and an inverting terminal thereof is connected between the resistor R3 and the diode D2. Also, in the differential band gap circuit, similarly to the current-mirror band gap circuit, the current, which flows into the output terminal VOUT, is discharged from the resistors R1, R2, and R3, and the diodes D1 and D2.
FIG. 11 is one example of a characteristic view illustrating power supply voltage dependency in the differential band gap circuit. In FIG. 11, the power supply voltage VDD was set in a transverse axis, and the voltage of the output terminal VOUT in an axis of ordinates. As shown in FIG. 11, it is necessary to apply an input voltage VDD of at least approx. 1.25 V to the input terminal in operating the conventional differential band gap circuit. At this time, the conventional differential band gap circuit operates with the output voltage VOUT thereof at approx. 1.25 V.
In such a manner, in the differential band gap circuit, the operation can be stably performed at a lower power supply voltage than it can be performed in the current-mirror band gap circuit. For this, in the event of operating the logic circuit at a low power supply voltage, the differential band gap circuit is utilized more frequently than the current-mirror band gap circuit. Furthermore, the differential band gap circuit, which is higher in the PSRR in a high-frequency region than the current-mirror band gap circuit because a negative feedback is applied with the differential amplifier, is employed in operating the logic circuit etc. at a high speed.
As mentioned before, in the conventional current-mirror band gap circuit and differential band gap circuit, the current that flows into the output terminal VOUT is discharged at the resistor and the diode. As it is, discharging ability of the resistor and the diode is poor in the conventional band gap circuit, whereby the current, which flows into the output terminal VOUT at the time of introducing the power supply and of fluctuation thereof, is impossible to discharge up. For this, the power supply rejection ratio (PSRR) lowers in the conventional band gap circuit.
Furthermore, in the conventional band gap circuit, being accompanied by development in low power consumption, the current that flows into the output terminal VOUT at the time of introducing the power supply and of fluctuation thereof is impossible to discharge up, whereby the problem exists that a stability time of the voltage at the output terminal VOUT at the time of starting is delayed and aggregated.
A reference voltage generator for quickly raising the reference voltage at the time of introducing the power supply voltage was disclosed in JP-P2002-123325A. However, the band gap circuit of JP-P2002-123325A, which is an electronic control device to be used for controlling an engine and an automatic transmission of an automobile etc., is a reference voltage generator for generating the reference voltage necessary for making an A/D conversion etc.
Also, there are many elements in the reference voltage generator of JP-P2002-123325A for the reason of its application, which are driven by employing a high-voltage power supply. For this, in the band gap apparatus of this reference voltage generator, in the event of driving the semiconductor integrated circuit at a high speed with the lower-voltage power supply, it becomes very difficult. For example, the voltage of 1.5 V is applied for driving in the recent year's high-speed band gap circuit employing the low-voltage power supply. To the contrary, in the reference voltage generator of JP-P2002-123325A, the voltage of 7 to 8 V or something like this is applied to the band gap circuit for driving, whereby the reference voltage generator in JP-P2002-123325A is impossible to drive by means of the low-voltage power supply.
In such a manner, in the conventional band gap circuit, the excess current that transitionally flows into the circuit output terminal is impossible to efficiently discharge in performing the operation at the low power supply voltage, whereby the problem existed that the PSRR lowered and furthermore the stability time of the voltage at the circuit output terminal was aggravated.